Halogenated hydrocarbon materials are burned in an internally fired horizontal fire tube boiler and the heat of combustion is extracted to produce saturated steam. Halogen values are recovered from the combustion of waste liquids and gases, such as by being absorbed in water. For efficient reclamation of halogen values combustion from highly chlorinated, low fuel value materials should occur at or near adiabatic conditions as possible and at minimal excess oxygen required for combustion. When more highly chlorinated hydrocarbon waste is incinerated, typically which is of lower fuel value, additional fuel feed is necessary for efficient combustion and the combustion temperature is typically higher than is normal for such fire tube boilers. The varying physical and chemical properties of waste feeds, corrosiveness of their combustion products, and the extreme operating temperature required for the effective destruction of toxic substances makes heat recovery a challenging problem. It has been found that commercial packaged steam boilers and incinerators equipped with conventional steam generating heat exchangers have certain deficiencies if fired with liquid waste and off-gases containing halogenated hydrocarbons. The substantially greater heat required for efficient combustion and the excessively corrosive nature of the flue gas generated by combustion have detrimental effect on the structure of boiler apparatus. The tube sheets of tube sheet boilers, when composed of conventional metals such as carbon steel are destroyed by corrosion by a relatively short period of time, requiring exceptional high maintenance cost for the equipment. Under circumstances where the fire tube boilers incorporate more exotic metals for corrosion resistance, the cost of the boiler itself becomes disadvantageously high.
It is considered desirable to utilize commercially packaged fire tube boilers for destruction of halogenated hydrocarbons and to utilize conventional end sheet metal material in order that boiler cost will remain as low as possible. It is also desirable however to provide suitable modifications which render standard fire tube boilers efficient for combustion of highly halogenated hydrocarbons.
When utilizing commercial fire tube boilers for incineration of highly chlorinated hydrocarbon waste materials it has been found that the volume of the combustion chamber (furnace) is too small to contain the typically larger flame that is needed and to provide sufficient residence time in the combustion chamber for the combustion of such wastes. Also these waste materials often have undesirable physical properties to make uniform feed control and atomization of the liquid into fine droplets difficult. As a result, the flame is unstable and is of such length that its contact with the refractory lining and/or metal heat transfer surfaces of the boiler causes failures or significantly reduces the service life of the boiler.
It is also known that liquid wastes of highly chlorinated hydrocarbons and off-gases have high quantity of inert materials and as a result have low caloric values. Firing these waste materials in the water cooled furnace of a packaged fire tube boiler ordinarily requires a high proportion of support fuel, such as natural gas or fuel oil, to waste feed to maintain a stable flame and sustain combustion for complete destruction of the organic waste.
In some cases an incinerator equipped with a conventional steam generating exchanger of the "straight through" variety of the general nature set forth in U.S. Pat. No. 4,198,384 may be employed to resolve the above problems regarding packaged fire tube boilers, but this type of incinerator also has an inherent problem. Extreme combustion temperatures of 1000.degree. C. to 1800.degree. C. (1200.degree. C. to 1500.degree. C. most common in practice) are required to successfully destroy toxic substances to a level required by government regulations. The front tube section of these straight through exchanger is subject to rapid failure when directly exposed to the hot combustion gases and the radiant heat from the refractory walls of the furnace. Special designs to reduce the tube sheet temperature and special materials of construction are required for this system to be successful. Obviously, special designs and exotic materials significantly increase the cost of straight through incinerators of this character and therefore render them commercially undesirable.
The present invention utilizes the advantages of a refractory lined furnace and also employs a large water cooled furnace interconnected with a fire tube boiler to reduce the combustion gas temperature in the boiler to a level sufficiently low (1000.degree. C. or so) that standard materials of construction and design may be employed for the tube sheets of the steam generator, thereby resulting in an incinerator construction of reasonable cost and efficient service-ability.
Very useful fire-tube boiler structures are set forth in U.S. Pat. Nos. 4,125,593, 4,195,596 and 4,476,791. Halogenated hydrocarbon materials from a waste feed can be routinely combusted in these fire-tube boiler structures. The present disclosure sets forth an improvement to such fire tube boiler systems wherein more highly chlorinated hydrocarbons of lower fuel value can be efficiently combusted for HCl recovery and steam generation through the use of standard boiler materials that are not diminished by the excessive corrosion that ordinarily occurs. Thus, this disclosure relates to a combustion chamber and fire tube boiler assembly which enables the incidental recovery of heat resulting from incineration of either liquid or gas waste materials (typically halogenated hydrocarbons) all accomplished in a manner satisfactory to regulatory authorities relating to such disposal.